Because of limitation of a transmission bandwidth and other conditions, currently, a frequency bandwidth of a voice signal transmitted on a main telephony network is generally less than 4 kHz, and a frequency band is generally limited to a range of 300 Hz to 3.4 kHz. As a communication bandwidth gradually increases, users impose an increasingly high requirement for voice quality and immersive experience. Consequently, a conventional narrowband voice can no longer meet an experience requirement of a user. In addition, lack of high frequency information in a conventional telephony voice greatly affects users with hearing impairments, and it is usually difficult for the users with hearing impairments to talk over a telephone. Therefore, a wideband voice, even a super wideband voice, and the like become increasingly popular.
Nowadays, 2nd generation (2G), 3rd generation (3G), and 4th generation (4G) networks coexist, and therefore terminals that support various voice bandwidths may coexist. For example, a narrowband terminal with a maximum support capability for a narrowband (NB, Narrowband) voice bandwidth, a wideband terminal with a maximum support capability for a wideband (WB, Wideband) voice bandwidth, a super wideband terminal with a maximum support capability for a super wideband (SWB, Super Wideband) voice bandwidth, and a full band terminal with a maximum support capability for a full band (FB, Full Band) voice bandwidth may coexist.
When a call is placed between two terminals that support a same maximum voice bandwidth, a corresponding voice signal bandwidth service may be established. However, when a call is placed between a terminal supporting a relatively narrow maximum voice bandwidth (for example, NB) and a terminal supporting a relatively wide maximum voice bandwidth (such as WB or SWB), in the conventional solution, the terminal (for example, a WB terminal) supporting a relatively wide maximum voice bandwidth usually can enjoy a voice bandwidth service that is only basically equal to a voice bandwidth service (for example, an NB bandwidth service) of the terminal (for example, an NB terminal) supporting a relatively narrow maximum voice bandwidth.